Cyanide is a rapid acting neurotoxic compound that can produce delayed neurodegeneration and a Parkinson-like syndrome. The brain exhibits differential susceptibility to cyanide in which the parietal and suprarhinal motor cortex (CX) undergo apoptotic cell death and necrotic cell death [occurs] in the substantia nigra (SN). In cultured neurons, cyanide produces a unique, selective vulnerability resulting from activation of cell specific response pathways that produce apoptosis in CX cells and necrosis in SN cells. Cyanide stimulates excessive generation of reactive oxygen species and nitric oxide and the resultant oxidative stress is proposed to be a common initiator of the cytotoxicity. The proposed study will determine the initiation events of apoptosis and necrosis and the execution cascades resulting in different modes of death. A comparative study will be conducted in primary cultured CX and SN neurons to determine the intracellular cascades activated during cyanide-induced injury and determine the point at which the cascades diverge to produce either apoptosis or necrosis. This will include studying the constitutive expression or induction of enzymes involved in generation of oxidative stress (nitric oxide synthase, cyclo-oxygenase 2), pro-death signals (cytosolic cytochrome c, caspase family of proteases), anti-death signals (Bcl-2 family, superoxide dismutase) and redox sensitive transcription factors (AP-1, NF-kappa-B). In conducting rescue studies by removing cyanide or adding selective inhibitors of the cell death factors at specific times after toxic insult, the molecular order of events leading to the commitment to death will be determined. The control points in the intracellular cascades that determine the mode of cell death will be identified by over- or underexpressing dominant factors in the cell death cascades. The long term goal of this project is to identify the mechanisms underlying cyanide-induced apoptotic and necrotic cytotoxicity and understand why brain areas are selectively vulnerable to cyanide. Additionally, this study will provide fundamental information on xenobiotic-induced neurodegeneration and provide new insight on selective vulnerability of the nervous system.